The present invention relates generally to the identification, isolation, and recombinant production of a novel cytokine, designated herein as xe2x80x9cApa-2 ligandxe2x80x9d, which induces mammalian cell apoptosis, and to methods of using Apo-2 ligand.
Control of cell numbers in mammals is believed to be determined, in part, by a balance between cell proliferation and cell death. One form of cell death, sometimes referred to as necrotic cell death, is typically characterized as a pathologic form of cell death resulting from some trauma or cellular injury. In contrast, there is another, xe2x80x9cphysiologicxe2x80x9d form of cell death which usually proceeds in an orderly or controlled manner. This orderly or controlled form of cell death is often referred to as xe2x80x9capoptosisxe2x80x9d [see, e.g., Barr et al., Bio/Technology, 12:487-493 (1994)]. Apoptotic cell death naturally occurs in many physiological processes, including embryonic development and clonal selection in the immune system [Itoh et al., Cell, 66:233-243 (1991)]. Decreased levels of apoptotic cell death, however, have been associated with a variety of pathological conditions, including cancer, lupus, and herpes virus infection [Thompson, Science, 267:1456-1462 (1995)].
Apoptotic cell death is typically accompanied by one or more characteristic morphological and biochemical changes in cells, such as condensation of cytoplasm, loss of plasma membrane microvilli, segmentation of the nucleus, degradation of chromosomal DNA or loss of mitochondrial function. A variety of extrinsic and intrinsic signals are believed to trigger or induce such morphological and biochemical cellular changes [Raff, Nature, 356:397-400 (1992); Steller, Science, 267:1445-1449 (1995); Sachs et al., Blood, 82:15 (1993)]. For instance, they can be triggered by hormonal stimuli, such as glucocorticoid hormones for immature thymocytes, as well as withdrawal of certain growth factors [Watanabe-Fukunaga et al., Nature, 356:314-317 (1992)]. Also, some identified oncogenes such as myc, rel, and ElA, and tumor suppressors, like p53, have been reported to have a role in inducing apoptosis. Certain chemotherapy drugs and some forms of radiation have likewise been observed to have apoptosis-inducing activity [Thompson, supra].
Various molecules, such as tumor necrosis factor-xcex1 (xe2x80x9cTNF-xcex1xe2x80x9d), tumor necrosis factor-xcex2 (xe2x80x9cTNF-xcex2xe2x80x9d or xe2x80x9clymphotoxinxe2x80x9d), CD30 ligand, CD27 ligand, CD40 ligand, OX-40 ligand, 4-1BB ligand, and Apo-1 ligand (also referred to as Fas ligand or CD95 ligand) have been identified as members of the tumor necrosis factor (xe2x80x9cTNFxe2x80x9d) family of cytokines [See, e.g., Gruss and Dower, Blood, 85:3378-3404 (1995)]. Among these molecules, TNF-xcex1, TNF-xcex2, CD30 ligand, 4-1BB ligand, and Apo-1 ligand have been reported to be involved in apoptotic cell death. Both TNF-xcex1 and TNF-xcex2 have been reported to induce apoptotic death in susceptible tumor cells [Schmid et al., Proc. Natl. Acad. Sci., 83:1881 (1986); Dealtry et al., Eur. J. Immunol., 17:689 (1987)]. Zheng et al. have reported that TNF-xcex1 is involved in post-stimulation apoptosis of CD8-positive T cells [Zheng et al., Nature, 377:348-351 (1995)]. Other investigators have reported that CD30 ligand may be involved in deletion of self-reactive T cells in the thymus [Amakawa et al., Cold Spring Harbor Laboratory Symposium on Programmed Cell Death, Abstr. No. 10, (1995)].
Mutations in the mouse Fas/Apo-1 receptor or ligand genes (called lpr and gld, respectively) have been associated with some autoimmune disorders, indicating that Apo-1 ligand may play a role in regulating the clonal deletion of self-reactive lymphocytes in the periphery [Krammer et al., Curr. Op. Immunol., 6:279-289 (1994); Nagata et al., Science, 267:1449-1456 (1995)]. Apo-1 ligand is also reported to induce post-stimulation apoptosis in CD4-positive T lymphocytes and in B lymphocytes, and may be involved in the elimination of activated lymphocytes when their function is no longer needed. [Krammer et al., supra; Nagata et al., supra]. Agonist mouse monoclonal antibodies specifically binding to the Apo-1 receptor have been reported to exhibit cell killing activity that is comparable to or similar to that of TNF-xcex1 [Yonehara et al., J. Exp. Med., 169:1747-1756 (1989)].
Induction of various cellular responses mediated by such TNF family cytokines is believed to be initiated by their binding to specific cell receptors. Two distinct TNF receptors of approximately 55-kDa (TNF-R1) and 75-kDa (TNF-R2) have been identified [Hohman et al., J. Biol. Chem., 264:14927-14934 (1989); Brockhaus et al., Proc. Natl. Acad. Sci., 87:3127-3131 (1990); EP 417,563, published Mar. 20, 1991] and human and mouse cDNAs corresponding to both receptor types have been isolated and characterized [Loetscher et al., Cell, 61:351 (1990); Schall et al., Cell, 61:361 (1990); Smith et al., Science, 248:1019-1023 (1990); Lewis et al., Proc. Natl. Acad. Sci., 88:2830-2834 (1991); Goodwin et al., Mol. Cell. Biol., 11:3020-3026 (1991)].
Itoh et al. disclose that the Apo-1 receptor can signal an apoptotic cell death similar to that signaled by the 55-kDa TNF-R1 [Itoh et al., supra]. Expression of the Apo-1 antigen has also been reported to be down-regulated along with that of TNF-R1 when cells are treated with either TNF-xcex1 or anti-Apo-1 mouse monoclonal antibody [Krammer et al., supra; Nagata et al., supra]. Accordingly, some investigators have hypothesized that cell lines that co-express both Apo-1 and TNF-R1 receptors may mediate cell killing through common signaling pathways [Id.].
The TNF family ligands identified to date, with the exception of lymphotoxin-xcex1, are type II transmembrane proteins, whose C-terminus is extracellular. In contrast, the receptors in the TNF receptor (TNFR) family identified to date are type I transmembrane proteins. In both the TNF ligand and receptor families, however, homology identified between family members has been found mainly in the extracellular domain (xe2x80x9cECDxe2x80x9d). Several of the TNF family cytokines, including TNF-xcex1, Apo-1 ligand and CD40 ligand, are cleaved proteolytically at the cell surface; the resulting protein in each case typically forms a homotrimeric molecule that functions as a soluble cytokine. TNF receptor family proteins are also usually cleaved proteolytically to release soluble receptor ECDs that can function as inhibitors of the cognate cytokines. For a review of the TNF family of cytokines and their receptors, see Gruss and Dower, supra.
Applicants have identified cDNA clones that encode a novel cytokine, designated xe2x80x9cApo-2 ligand.xe2x80x9d It is presently believed that Apo-2 ligand is a member of the TNF cytokine family; Apo-2 ligand is related in amino acid sequence to some known TNF-related proteins, including the Apo-1 ligand. Applicants found, however, that the Apo-2 ligand is not inhibited appreciably by known soluble Apo-1 or TNF receptors, such as the Fas/Apo-1, TNF-R1, or TNF-R2 receptors.
In one embodiment, the invention provides isolated biologically active Apo-2 ligand. In particular, the invention provides isolated biologically active human Apo-2 ligand, which in one embodiment, includes an amino acid sequence comprising residues 114-281 of FIG. 1A. In another embodiment, the Apo-2 ligand includes an amino acid sequence comprising residues 41-281 or 15-281 of FIG. 1A. In another embodiment, the isolated biologically active human Apo-2 ligand includes an amino acid sequence shown as residues 1-281 of FIG. 1A (SEQ ID NO:1).
In another embodiment, the invention provides chimeric molecules comprising Apo-2 ligand fused to another, heterologous polypeptide. An example of such a chimeric molecule comprises the Apo-2 ligand fused to a tag polypeptide sequence.
In another embodiment, the invention provides an isolated nucleic acid molecule encoding Apo-2 ligand. In one aspect, the nucleic acid molecule is RNA or DNA that encodes a biologically active Apo-2 ligand or is complementary to nucleic acid sequence encoding such Apo-2 ligand, and remains stably bound to it under stringent conditions. In one embodiment, the nucleic acid sequence is selected from:
(a) the coding region of the nucleic acid sequence of FIG. 1A that codes for the full-length protein from residue 1 to residue 281 (i.e., nucleotides 91 through 933), inclusive, or nucleotides 211 through 933 that encodes for the extracellular protein from residue 41 to 281, inclusive, or nucleotides 430 through 933 that encodes for the extracellular protein from residue 114 to 281, inclusive, of the nucleic acid sequence shown in FIG. 1A (SEQ ID NO:2); or
(b) a sequence corresponding to the sequence of (a) within the scope of degeneracy of the genetic code.
In a further embodiment, the invention provides a replicable vector comprising the nucleic acid molecule encoding the Apo-2 ligand operably linked to control sequences recognized by a host cell transfected or transformed with the vector. A host cell comprising the vector or the nucleic acid molecule is also provided. A method of producing Apo-2 ligand which comprises culturing a host cell comprising the nucleic acid molecule and recovering the protein from the host cell culture is further provided.
In another embodiment, the invention provides an antibody which binds to the Apo-2 ligand.
In another embodiment, the invention provides a composition comprising biologically active Apo-2 ligand and a pharmaceutically-acceptable carrier. The composition may be a pharmaceutical composition useful for inducing or stimulating apoptosis.
In another embodiment, the invention provides a method for inducing apoptosis in mammalian cells, comprising exposing mammalian cells, in vivo or ex vivo, to an amount of Apo-2 ligand effective for inducing apoptosis.
In another embodiment, the invention provides methods of treating a mammal having cancer. In the methods, an effective amount of Apo-2 ligand is administered to a mammal diagnosed as having cancer. The Apo-2 ligand may also be administered to the mammal along with one or more other therapies, such as chemotherapy, radiation therapy, or other agents capable of inducing apoptosis.
A further embodiment of the invention provides articles of manufacture and kits that include Apo-2 ligand or Apo-2 ligand antibodies. The articles of manufacture and kits include a container, a label on the container, and a composition contained within the container. The label on the container indicates that the composition can be used for certain therapeutic or non-therapeutic applications. The composition contains an active agent, and the active agent comprises Apo-2 ligand or Apo-2 ligand antibodies.